Robot joint structure

ABSTRACT

According to a certain aspect of the present invention, a control device for a robot is provided. The control device includes a processor configured to implement: a function of obtaining a signal indicating a detected value of a sensor detecting a state quantity of the robot; and a function of, in converting the detected value to an estimated value of the state quantity according to a conversion function obtained by calibration of the sensor, applying an offset value compensating for a difference between the estimated value and the actual state quantity in a critical situation in operation of the robot.

TECHNICAL FIELD

The present invention relates to a joint structure for a robot.

BACKGROUND ART

A robot can be made to perform various operations such as thoseperformed by a human, for example, by providing the robot with astructure such as an arm, a leg, or the like formed by a link and ajoint portion, and rotation-driving the joint portion by an actuator.

For example, PTL 1 describes a robot that performs whole-bodycoordinated movement by having a head portion, a trunk portion, an armportion, a hand portion, and a leg portion, and driving a joint portionof each of these portions by an actuator.

CITATION LIST Patent Literature

[PTL 1] U.S. Patent Application Publication No. 2013/0202212

SUMMARY Technical Problem

In order to stabilize the operation of the robot as described above, itis desirable to prevent the occurrence of an unexpected moment orvibration during the operation of the robot, for example. In actuality,however, it is not necessarily easy to stabilize the operation of therobot by preventing the occurrence of an unexpected moment or vibrationbecause of a backlash or the like present in the joint portion, amechanism for transmitting a driving force to the joint portion, or thelike.

It is accordingly an object of the present invention to provide a newand improved joint structure for a robot which joint structure makes itpossible to stabilize the operation of a robot by appropriatelycontrolling a backlash that can occur in a joint portion of the robot.

Solution to Problem

According to a certain aspect of the present invention, a control devicefor a robot is provided. The control device includes a processorconfigured to implement: a function of obtaining a signal indicating adetected value of a sensor detecting a state quantity of the robot; anda function of, in converting the detected value to an estimated value ofthe state quantity according to a conversion function obtained bycalibration of the sensor, applying an offset value compensating for adifference between the estimated value and the actual state quantity ina critical situation in operation of the robot.

According to the configuration of the present invention as describedabove, it is possible to stabilize the operation of a robot byappropriately controlling a backlash that can occur in a joint portionof the robot.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustrative diagram depicting a joint configuration of arobot according to one embodiment of the present invention.

FIG. 2 is an illustrative diagram depicting a hardware configuration ofthe robot according to one embodiment of the present invention.

FIG. 3 is an illustrative block diagram depicting a configuration fordriving a joint portion of the robot according to one embodiment of thepresent invention.

FIG. 4 is a diagram of assistance in explaining an example of a typicalbacklash.

FIG. 5A is a diagram of assistance in explaining an example of abacklash in the joint portion of the robot.

FIG. 5B is a diagram of assistance in explaining the example of thebacklash in the joint portion of the robot.

FIG. 6A is a diagram of assistance in explaining an example of an effectof a backlash in the bipedal walking of the robot.

FIG. 6B is a diagram of assistance in explaining the example of theeffect of the backlash in the bipedal walking of the robot.

FIG. 6C is a diagram of assistance in explaining the example of theeffect of the backlash in the bipedal walking of the robot.

FIG. 7 is a diagram depicting an example of a joint structure of therobot according to one embodiment of the present invention.

FIG. 8A is a diagram of assistance in explaining an example ofapplication of the joint structure in leg portions of the robotaccording to one embodiment of the present invention.

FIG. 8B is a diagram of assistance in explaining the example ofapplication of the joint structure in the leg portions of the robotaccording to one embodiment of the present invention.

FIG. 9A is a diagram of assistance in explaining an example ofapplication of the joint structure in arm portions of the robotaccording to one embodiment of the present invention.

FIG. 9B is a diagram of assistance in explaining the example ofapplication of the joint structure in the arm portions of the robotaccording to one embodiment of the present invention.

FIG. 10A is a diagram depicting a modification of the joint structure ofthe robot according to one embodiment of the present invention.

FIG. 10B is a diagram depicting a modification of the joint structure ofthe robot according to one embodiment of the present invention.

FIG. 11 is a graph of assistance in explaining an example of calibrationof a potentiometer.

FIG. 12 is a graph of assistance in explaining application of an offsetvalue to a potentiometer calibration result in one embodiment of thepresent invention.

FIG. 13 is a flowchart depicting an example of a concrete procedure forsetting and applying the offset value in one embodiment of the presentinvention.

FIG. 14 is a graph of assistance in explaining an example of selectivelyapplying a plurality of offset values to a potentiometer calibrationresult in one embodiment of the present invention.

FIG. 15 is a flowchart depicting an example of a concrete procedure forselectively applying the plurality of offset values in one embodiment ofthe present invention.

DESCRIPTION OF EMBODIMENTS

A few embodiments of the present invention will hereinafter be describedin detail with reference to the accompanying drawings. Incidentally, inthe present specification and the drawings, constituent elements havingessentially identical functional configurations are identified by thesame reference numerals, and repeated description thereof will beomitted.

(Joint Configuration of Robot)

FIG. 1 is an illustrative diagram depicting a joint configuration of arobot according to one embodiment of the present invention. Referring toFIG. 1, a robot 10 according to one illustrative embodiment of thepresent invention includes a head portion 101, a main body portion 102,a pair of arm portions 103L and 103R, a pair of hand portions 104L and104R, a pair of leg portions 105L and 105R, and a pair of foot portions106L and 106R. Each of these parts includes a joint portion and a linkcoupled to the joint portion. The link relatively rotates about thejoint portion. Various kinds of operation of the robot 10 are therebyrealized.

In the illustrated example, the left arm portion 103L includes ashoulder joint portion 131L, an elbow joint portion 132L, and a wristjoint portion 133L. The shoulder joint portion 131L is located between ashoulder link 141L coupled to the main body portion 102 and an upper armlink 142L. The shoulder joint portion 131L enables relative rotation ofthe link 142L with respect to the link 141L. More specifically, thejoint portion 131L includes a pitch joint portion 131L_P enabling pitchrotation, a roll joint portion 131L_R enabling roll rotation, and a yawjoint portion 131L_Y enabling yaw rotation. Incidentally, in the presentspecification, rotational axes (pitch, roll, and yaw) are defined withthe upright posture of the robot 10 as a reference. The structure ofsuch a joint portion 131L enables the upper arm link 142L to rotate ineach direction with respect to the shoulder link 141L.

Similarly, the elbow joint portion 132L is located between the upper armlink 142L and a forearm link 143L. The elbow joint portion 132L includesa pitch joint portion 132L_P enabling pitch rotation and a yaw jointportion 132L_Y enabling yaw rotation. The structure of such a jointportion 132L enables the forearm link 143L to rotate in a pitchdirection and a yaw direction with respect to the upper arm link 142L.In addition, the wrist joint portion 133L is located between the forearmlink 143L and a wrist link 144L coupled to the hand portion 104L. Thewrist joint portion 133L includes a roll joint portion 133L_R enablingroll rotation and a pitch joint portion 133L_P enabling pitch rotation.The structure of such a joint portion 133L enables the wrist link 144Lto rotate in a roll direction and a pitch direction with respect to theforearm link 143L.

In addition, in the illustrated example, the left leg portion 105Lincludes a crotch joint portion 134L, a knee joint portion 135L, and anankle joint portion 136L. The crotch joint portion 134L is locatedbetween a waist link 145 coupled to the main body portion 102 and athigh link 146L. The crotch joint portion 134L enables relative rotationof the link 146L with respect to the link 145. More specifically, thejoint portion 134L includes a yaw joint portion 134L_Y enabling yawrotation, a roll joint portion 134L_R enabling roll rotation, and apitch joint portion 134L_P enabling pitch rotation. The structure ofsuch a joint portion 134L enables the thigh link 146L to rotate in eachdirection with respect to the waist link 145.

Similarly, the knee joint portion 135L is located between the thigh link146L and a crus link 147L. The knee joint portion 135L includes a pitchjoint portion 135L_P enabling pitch rotation. The structure of such ajoint portion 135L enables the crus link 147L to rotate in a pitchdirection with respect to the thigh link 146L. In addition, the anklejoint portion 136L is located between the crus link 147L and an anklelink 148L coupled to the foot portion 106L. The ankle joint portion 136Lincludes a pitch joint portion 136L_P enabling pitch rotation and a rolljoint portion 136L_R enabling a roll joint portion. The structure ofsuch a joint portion 136L enables the ankle link 148L to rotate in apitch direction and a roll direction with respect to the crus link 147L.

Incidentally, in the illustrated example, the configuration of the rightarm portion 103R and the right leg portion 105R is similar to theconfiguration of the left arm portion 103L and the left leg portion 105Ldescribed above, and therefore repeated description thereof will beomitted. Specifically, the right arm portion 103R includes a shoulderjoint portion 131R coupled to a shoulder link 141R, an upper arm link142R coupled to the shoulder joint portion 131R, an elbow joint portion132R coupled to the upper arm link 142R, a forearm link 143R coupled tothe elbow joint portion 132R, a wrist joint portion 133R coupled to theforearm link 143R, and a wrist link 144R coupled to the wrist jointportion 133R and the hand portion 104R. The right leg portion 105Rincludes a crotch joint portion 134R coupled to the waist link 145, athigh link 146R coupled to the crotch joint portion 134R, a knee jointportion 135R coupled to the thigh link 146R, a crus link 147R coupled tothe knee joint portion 135R, an ankle joint portion 136R coupled to thecrus link 147R, and an ankle link 148R coupled to the ankle jointportion 136R and the foot portion 106R.

(Hardware Configuration of Robot)

FIG. 2 is an illustrative diagram depicting a hardware configuration ofthe robot according to one embodiment of the present invention.Referring to FIG. 2, the robot 10 has a control device 110 included inthe main body portion 102. The control device 110 includes a centralprocessing unit (CPU) 111 performing arithmetic processing, a randomaccess memory (RAM) 112, a read only memory (ROM) 113, an externalmemory 114, and the like. The control device 110 determines theoperation of the robot 10 according to image data generated by a camera121, audio data generated by a microphone 122, a command signal receivedby a communication interface 124, or the like. The camera 121, themicrophone 122, and the communication interface 124 are connected to thecontrol device 110 via a bus interface 115.

Here, the camera 121 as an example of an image input device includes animaging element, a lens, and an image processing circuit. The camera 121generates image data obtained by capturing an image of the periphery ofthe robot 10. The microphone 122 as an example of a sound input devicegenerates audio data obtained by capturing sound of the periphery of therobot. The communication interface 124 performs communication by wire orradio with an external device, and thereby transmits and receivesvarious kinds of signals and data to and from the external device.Specifically, the communication interface 124 may transmit and receivesignals to and from a terminal device functioning as a remote controllerof the robot 10, the terminal device being, for example, a smart phone,a tablet, or a dedicated controller, by wireless communication usingBluetooth (registered trademark), a wireless local area network (LAN),infrared rays, or the like. In addition, the communication interface 124may be connected to a network via the external device, and transmit andreceive signals to and from a server on the network.

In addition, the control device 110 controls each part of the robot 10so as to perform a determined operation. Specifically, the controldevice 110 controls motors 150 that rotation-drive the joint portions ofthe arm portions 103L and 103R, the hand portions 104L and 104R, and theleg portions 105L and 105R so as to perform the determined operation.Though not depicted, a joint portion driven by a motor 150 may beprovided also to the head portion 101, the main body portion 102, andthe foot portions 106L and 106R. At this time, the control device 110refers to detected values of a distance measuring sensor (not depicted),an inertial measurement unit (IMU) 125, grounding confirming sensors126L and 126R, a load sensor (not depicted), and a power control device127 as required. In addition, the control device 110 may provide audiodata to a speaker 123 or transmit a command signal from thecommunication interface 124 to the external device so as to perform thedetermined operation. The speaker 123, the communication interface 124,the motor 150, the distance measuring sensor, the IMU 125, the groundingconfirming sensors 126L and 126R, the load sensor, and the power controldevice 127 are connected to the control device 110 via the bus interface115.

Here, the distance measuring sensor detects a distance to an objectpresent on the periphery of the robot 10. The IMU 125 detects theposture and inclination of the main body portion 102. The groundingconfirming sensors 126L and 126R detect contact of the foot portions106L and 106R with a floor surface. The load sensor detects a loadapplied to each of the foot portions 106L and 106R. The power controldevice 127 is used to manage a power supply such as a battery or thelike, and detects a remaining capacity of the power supply.

For example, the CPU 111 of the control device 110 selects a patterncorresponding to the determined operation from control patterns storedin the ROM 113 or the external memory 114, sets a foot portion movement,a zero moment point (ZMP) trajectory, a trunk movement, an upper limbmovement, the horizontal position and height of the waist portion, andthe like according to the selected pattern, and controls the motors 150according to these set values. At this time, the CPU 111 may adaptivelycontrol the motors 150 according to the detected values of the sensorsas described above or the like.

(Configuration for Driving Joint Portion)

FIG. 3 is an illustrative block diagram depicting a configuration fordriving a joint portion of the robot according to one embodiment of thepresent invention. Referring to FIG. 3, the robot 10 includes a servocircuit 151, a driver 152, an encoder 153, a driving force transmittingmechanism 154, a potentiometer 155, and an analog/digital (A/D)converter circuit 156 in addition to the control device 110 and a motor150 as a configuration for driving a joint portion 130 (joint portionsof the robot 10 as depicted in FIG. 1 will hereinafter be collectivelyreferred to also as the joint portion 130). The control device 110inputs a target value of a rotational angle of the motor 150 to theservo circuit 151. The servo circuit 151 drives the motor 150 byinputting a control signal to the driver 152, and detects the rotationalangle of the motor 150 on the basis of a pulse signal output from theencoder 153 as the motor 150 rotates. The servo circuit 151 adjusts thecontrol signal input the driver 152 such that the rotational anglereaches the target value.

The driving force transmitting mechanism 154 transmits a rotationaldriving force of the motor 150 to the joint portion 130. A relativerotation thereby occurs between two links coupled to the joint portion130 (for example, the waist link 145 and the thigh link 146L in a caseof the crotch joint portion 134L depicted in FIG. 1). The potentiometer155 is attached to the joint portion 130 so as to detect this relativerotation. Hence, when the above-described relative rotation occurs, anoutput voltage of the potentiometer 155 changes according to therotational angle. The control device 110 obtains a digital signalgenerated by the A/D converter circuit 156 on the basis of the outputvoltage.

In the control device 110, the CPU 111 calculates the rotational angledetected by the potentiometer 155 on the basis of the signal input fromthe A/D converter circuit 156. At this time, the CPU 111 refers to aconversion function 116 stored in the ROM 113 or the external memory114. Further, as required, the CPU 111 refers to an offset value 117stored in the ROM 113 or the external memory 114 separately from theconversion function 116. Incidentally, details of the conversionfunction 116 and the offset value 117 will be described later. Bycomparing the target value of the rotational angle of the motor 150, thetarget value being input to the servo circuit 151 by the control device110, with a result of the calculation of the rotational angle detectedby the potentiometer 155, it is possible to extract a difference betweenan ideal value of the rotational angle of the joint portion 130 (forexample, a rotational angle considered to be necessary for the robot 10to perform a predetermined operation) and the actually occurringrotational angle. In a case where the difference is large, for example,the control device 110 inputs an additional target value forcompensating for the difference to the servo circuit 151.

Incidentally, in the robot 10 according to the present embodiment, thefeedback of the rotational angle by the potentiometer 155 does notnecessarily need to be performed at all of the joint portion 130, andthe potentiometer 155 and the A/D converter circuit 156 may not beattached to at least a part of the joint portions. In addition, thedifference between the ideal value of the rotational angle and theactually occurring rotational angle may be estimated by detecting theposture and inclination of the robot 10 from a detected value of anothersensor such as the IMU 125 depicted in FIG. 2 or the like instead ofdetecting the actual rotational angle by the potentiometer 155.

(Backlash in Joint Structure)

A backlash refers to a gap present in an engaging portion of a machineelement such as a gear or the like. In general, a backlash of anappropriate magnitude is intentionally provided to enable smoothmovement of the machine element. However, the backlash may increase toexceed an appropriate range due to wear of the member.

FIG. 4 is a diagram of assistance in explaining an example of a typicalbacklash. As depicted in FIG. 4, in a case of rotating an object OBJsymmetric with respect to a rotational axis, the object OBJ being, forexample, a wheel, a turn table, or the like, the position of a backlashBL is determined by the direction of rotation driving. Specifically, asdepicted in the figure, the backlash BL occurs at a position such thatthe rotation of a driving side element E₁ precedes the rotation of adriven side element E₂. When the direction of the rotation driving isreversed, positional relation between the driving side element E₁, thedriven side element E₂, and the backlash BL is reversed, and therefore arotation-driving dead band corresponding to the magnitude of thebacklash BL occurs.

FIG. 5A and FIG. 5B are diagrams of assistance in explaining an exampleof a backlash in a joint portion of the robot. FIG. 5A and FIG. 5Bdepict a main body side link 140A of the robot 10 (links coupled to themain body side of the joint portion 130 among the links of the robot 10as depicted in FIG. 1 will hereinafter be collectively referred to alsoas the main body side link 140A), the joint portion 130, and a distalside link 140B (links coupled to the distal side of the joint portion130 among the links of the robot 10 as depicted in FIG. 1 willhereinafter be collectively referred to also as the distal side link140B). The joint portion 130 includes a first part 130A coupled to themain body side link 140A and a second part 130B coupled to the distalside link 140B. Incidentally, the second part 130B is capable ofrelative rotation with respect to the first part 130A.

Here, in the example depicted in FIG. 5A and FIG. 5B, a rotationaldriving force transmitted by the driving force transmitting mechanism154, which is described with reference to FIG. 3 described above,effects a relative rotation of the second part 130B with respect to thefirst part 130A. As a result, the distal side link 140B rotates relativeto the main body side link 140A. At this time, the distal side link 140Bas a rotation target object is not symmetric with respect to arotational axis. Hence, the position of the backlash BL is determined bythe direction of a force F acting on the distal side link 140B ratherthan the direction of the rotation driving.

Specifically, in the example of FIG. 5A, a force F that causes a momentin an opposite direction from that of the rotation driving acts on thedistal side link 140B, and therefore a backlash BL such that therotation of the first part 130A precedes the rotation of the second part130B occurs as in the example of FIG. 4 described above. In the exampleof FIG. 5B, on the other hand, a force F that causes a moment in thesame direction as the rotation driving acts on the distal side link140B, and therefore a backlash BL such that the rotation of the secondpart 130B precedes the rotation of the first part 130A occurs unlike theexamples of FIG. 4 and FIG. 5A.

(Effect of Backlash in Bipedal Walking)

FIGS. 6A to 6C are diagrams of assistance in explaining an example of aneffect of a backlash in bipedal walking of the robot. These figuresdepict changes in backlashes BL occurring in the crotch roll jointportions 134L_R and 134R_R when the robot 10 performs bipedal walking.Incidentally, for simplicity, a pitch joint portion and a yaw jointportion that do not produce roll rotation are not depicted. In addition,backlashes occurring in the ankle roll joint portions 136L_R and 136R_Rare not depicted either.

FIG. 6A depicts a state in which the robot 10 moves the center ofgravity of the robot 10 to a right side in a stage before raising theleft leg portion 105L in bipedal walking. In this state, the own weightof the robot 10 is supported by both of the left and right leg portions105L and 105R. Hence, an upward reaction force from the floor surfaceacts on the left and right thigh links 146L and 146R (corresponding tothe distal side link 140B in the example of FIG. 5A and FIG. 5Bdescribed above). As a result, backlashes as depicted in the figureoccur in the roll joint portions 134L_R and 134R_R. Specifically, aninside backlash BL_(IN) occurs in the left roll joint portion 134L_R,and an outside backlash BL_(OUT) occurs in the right roll joint portion134R_R.

FIG. 6B depicts a state in which the robot 10 has raised the left legportion 105L after the state depicted in FIG. 6A. In this state, the ownweight of the robot 10 is supported by the right leg portion 105R.Hence, the upward reaction force from the floor surface continues to acton the right thigh link 146R, and the outside backlash BL_(OUT) occursin the right roll joint portion 134R_R. On the other hand, the reactionforce from the floor surface no longer acts on the left thigh link 146L.In this state, the link 146L constitutes a (slanted) cantilever havingthe left roll joint portion 134L_R as a fulcrum. Hence, a downwardgravity applied to the link 146L itself and the distal side parts of theleg portion 105L which parts are coupled to the link 146L (that is, theknee joint portion 135L, the crus link 147L, the ankle joint portion136L, the ankle link 148L, and the foot portion 106L) acts on the link146L. As a result, the backlash occurring in the left roll joint portion134L_R changes from the inside backlash BL_(IN) depicted in FIG. 6A toan outside backlash BL_(OUT).

FIG. 6C depicts a state in which the robot 10 has lowered the left legportion 105L to the floor surface after the state depicted in FIG. 6B.In this state, when the left foot portion 106L comes into contact withthe floor surface again, the own weight of the robot 10 is supported byboth of the left and right leg portions 105L and 105R. However, at thistime point, the backlash occurring in the left roll joint portion 134L_Rswitches from the outside backlash BL_(OUT) to the inside backlashBL_(IN) again, and therefore a dead band accompanying the switchingoccurs. During this period, an unstable backlash BL_(UNST) occurs in theleft roll joint portion 134L_R (that is, the backlash is present but theposition of the backlash is not stable), and there is a possibility ofalternate and irregular occurrence of a state in which the reactionforce from the floor surface acts on the left thigh link 146L and astate in which the reaction force from the floor surface does not act onthe left thigh link 146L. There is consequently a possibility that anunexpected moment is applied to the robot 10 including the leg portions105L and 105R or a vibration occurs in the robot 10, and that the robot10 thereby topples over.

(Example of Joint Structure of Robot)

FIG. 7 is a diagram depicting an example of a joint structure of therobot according to one embodiment of the present invention. Referring toFIG. 7, a joint structure 160 of the robot 10 includes the joint portion130 including the first part 130A and the second part 130B, the drivingforce transmitting mechanism 154, and a tension spring 161. Here, asdescribed above with reference to FIG. 5A and FIG. 5B, the first part130A of the joint portion 130 is coupled to the main body side link140A, and the second part 130B of the joint portion 130 is coupled tothe distal side link 140B.

Here, the main body side link 140A refers to a link that is one of thelinks coupled to the joint portion 130 and which is on a side closer tothe main body portion 102 of the robot 10. Similarly, the distal sidelink 140B refers to a link that is one of the links coupled to the jointportion 130 and which is on a side more distant from the main bodyportion 102. Specifically, in the case of the left leg portion 105L, asfor the crotch joint portion 134L, the waist link 145 corresponds to themain body side link 140A, and the thigh link 146L corresponds to thedistal side link 140B. As for the knee joint portion 135L, the thighlink 146L corresponds to the main body side link 140A, and the crus link147L corresponds to the distal side link 140B. As for the ankle jointportion 136L, the crus link 147L corresponds to the main body side link140A, and the ankle link 148L corresponds to the distal side link 140B.

As is understood from the above-described example, a same link can bethe main body side link 140A and can be the distal side link 140B,depending on with which joint portion of the robot 10 the joint portion130 is associated. While description has been made by taking the jointportions of the left leg portion 105L as an example in the foregoing,the same is true for the joint portions of the right leg portion 105R.In addition, the main body side link 140A and the distal side link 140Bcan be similarly defined in the arm portions 103L and 103R.Specifically, in the case of the left arm portion 103L, as for theshoulder joint portion 131L, the shoulder link 141L corresponds to themain body side link 140A, and the upper arm link 142L corresponds to thedistal side link 140B. As for the elbow joint portion 132L, the upperarm link 142L corresponds to the main body side link 140A, and theforearm link 143L corresponds to the distal side link 140B. As for thewrist joint portion 133L, the forearm link 143L corresponds to the mainbody side link 140A, and the wrist link 144L corresponds to the distalside link 140B. Similar definitions are also possible in the right sidearm portion 103R.

In other words, the distal side link 140B is a link that can constitutea cantilever having the joint portion 130 as a fulcrum. For example, inthe state depicted in FIG. 6B in the foregoing, the thigh link 146L asthe distal side link with respect to the crotch joint portion 134Lincluding the left roll joint portion 134L_R constitutes a cantileverhaving the joint portion 134L as a fulcrum. Specifically, while the footportion 106L is raised and separated from the floor surface, a first endportion of the link 146L is supported by the joint portion 134L, whereasa second end portion on an opposite side of the link 146L receives aload of the crus link 147L, the ankle joint portion 136L, the ankle link148L, and the foot portion 106L via the knee joint portion 135L.

The crus link 147L similarly constitutes a cantilever having the kneejoint portion 135L as a fulcrum. In addition, the ankle link 148Lconstitutes a cantilever having the ankle joint portion 136L as afulcrum. As in the foregoing, when the right leg portion 105R is raisedin a bipedal walking operation of the robot 10, the thigh link 146R onthe right side constitutes a cantilever having the crotch joint portion134R as a fulcrum, the crus link 147R constitutes a cantilever havingthe knee joint portion 135R as a fulcrum, and the ankle link 148Rconstitutes a cantilever having the ankle joint portion 136R as afulcrum. In addition, in the arm portions 103L and 103R, each link thatcan be the distal side link 140B as described above constitutes acantilever having the joint portion 130 as a fulcrum except for caseswhere the hand portions 104L and 104R are supported by an object otherthan the robot 10, for example.

As described above, the joint portion 130 includes the first part 130Acoupled to the main body side link 140A and the second part 130B coupledto the distal side link 140B. The first part 130A and the second part130B are assembled so as to be capable of rotating relative to eachother about the rotational axis X directly or via another part of thejoint portion 130. Relative rotation of the distal side link 140B withrespect to the main body side link 140A in the joint portion 130 isthereby made possible. The driving force transmitting mechanism 154transmits a rotational driving force for effecting relative rotation ofthe second part 130B with respect to the first part 130A about therotational axis X from the motor 150 described above with reference toFIG. 3 to the joint portion 130.

Here, while the driving force transmitting mechanism 154 is depictedincluding a chain or a belt, the driving force transmitting mechanism154 does not necessarily need to include a chain or a belt. The drivingforce transmitting mechanism 154 can include various kinds of machineelements such as a gear and the like. Even if the motor 150 is embeddedin the joint portion 130, an engaging portion of at least one set ofmachine elements constituting the driving force transmitting mechanism154 is present between the motor 150 and the joint portion 130. Due to abacklash provided to the engaging portion, a phenomenon as describedabove with reference to FIG. 5A and FIG. 5B and FIGS. 6A to 6C, forexample, occurs.

The tension spring 161 included in the joint structure 160 in thepresent embodiment is an example of biasing means for applying, to thesecond part 130B of the joint portion 130, a rotational biasing forceabout the rotational axis X, that is, a rotational biasing force coaxialwith the relative rotation of the second part 130B with respect to thefirst part 130A. In the illustrated example, both ends of the tensionspring 161 are respectively coupled to the main body side link 140A andthe distal side link 140B. The tension spring 161 is attached betweenthe main body side link 140A and the distal side link 140B in a state ofbeing expanded in advance. A tensile biasing force therefore occurs soas to rotate the distal side link 140B and bring the distal side link140B close to the main body side link 140A. As described above, the mainbody side link 140A and the distal side link 140B are respectivelycoupled to the first part 130A and the second part 130B of the jointportion 130. Thus, a rotational biasing force coaxial with the relativerotation of the second part 130B with respect to the first part 130A isprovided by the biasing force that the tension spring 161 applies to themain body side link 140A and the distal side link 140B as describedabove.

Consequently, in the illustrated example, unlike the example describedabove with reference to FIG. 5A, although a force F that causes a momentin an opposite direction from rotation driving acts on the distal sidelink 140B, a backlash BL occurs such that the rotation of the secondpart 130B precedes the rotation of the first part 130A. Here, as in theexample described with reference to FIG. 5B, a backlash BL occurs suchthat the rotation of the second part 130B precedes the rotation of thefirst part 130A also when a force F that causes a moment in the samedirection as the rotation driving acts on the distal side link 140B.That is, in the example depicted in FIG. 7, the position of the backlashBL does not change irrespective of the direction of the force acting onthe distal side link 140B.

(Example of Application of Joint Structure in Leg Portions)

FIG. 8A and FIG. 8B are diagrams of assistance in explaining an exampleof application of the joint structure 160 described above with referenceto FIG. 7 in the leg portions 105L and 105R of the robot 10 according toone embodiment of the present invention. FIG. 8A depicts a state similarto that depicted in FIG. 6B in the foregoing, that is, a state in whichthe robot 10 has raised the left leg portion 105L from the floor surfacein bipedal walking. In the example of FIG. 6B, the backlash occurring inthe left roll joint portion 134L_R in this state changes from the insidebacklash BL_(IN) to the outside backlash BL_(OUT). In the example ofFIG. 8A, the inside backlash BL_(IN) continues to occur in the rolljoint portion 134L_R even after the left leg portion 105L is raised.This is because in the joint structure 160 including the roll jointportion 134L_R, the tension spring 161 is attached so as to provide arotational biasing force that counters the gravity acting on the link146L when the thigh link 146L constitutes a cantilever having the rolljoint portion 134L_R as a fulcrum.

On the other hand, FIG. 8B depicts a state similar to that depicted inFIG. 6C in the foregoing, that is, a state in which the robot 10 haslowered the left leg portion 105L to the floor surface. In the exampleof FIG. 6C, an unstable backlash BL_(UNST) occurs as the backlashoccurring in the left roll joint portion 134L_R in this state changesfrom the outside backlash BL_(OUT) to the inside backlash BL_(IN) again.On the other hand, in the example of FIG. 8B, the inside backlashBL_(IN) occurs in the roll joint portion 134L_R also while the left legportion 105L is raised as described above, and therefore the backlashdoes not change again when the left leg portion 105L is lowered to thefloor surface. Hence, occurrence of an unexpected moment and vibrationdue to the occurrence of the unstable backlash BL_(INST) is prevented.

Thus, in one embodiment of the present invention, the tension spring 161in the joint structure 160 as described with reference to FIG. 7provides a rotational biasing force that counters the gravity acting onthe distal side link 140B that constitutes a cantilever having the jointportion 130 as a fulcrum. It is thereby possible to avoid destabilizingthe operation of the robot 10 due to the changing of the backlash in thejoint portion 130 when the distal side link 140B makes a transition froma state of not constituting a cantilever (state of being supported by apart other than the joint portion 130) to a state of constituting acantilever (state of being supported by only the joint portion 130).

Incidentally, while description has been made of the joint structure 160including the left crotch roll joint portion 134L_R in the example ofFIG. 8A and FIG. 8B described above, the joint structure 160 includingthe tension spring 161 can be similarly applied also to the left ankleroll joint portion 136L_R. When a similar joint structure 160 is appliedalso to the roll joint portion 134R_R (and the roll joint portion136R_R) included in the right leg portion 105R, an operation at a timeof raising the right leg portion 105R in bipedal walking can bestabilized. In addition, while description has been made by taking as anexample joint portions enabling roll rotation between links in the legportions 105L and 105R in FIG. 8A and FIG. 8B, the above-described jointstructure 160 can be similarly applied also to joint portions enablingpitch rotation and yaw rotation.

Here, joint portions of the leg portions 105L and 105R of the robot 10to which joint portions to apply the joint structure 160 may, forexample, be determined as follows. For example, the crotch roll jointportions 134L_R and 134R_R in the above-described example are jointportions in which changing of the backlash may destabilize the operationof the robot 10 because timing in which the supporting of one legchanges to the supporting of two legs (or vice versa) in bipedal walkingof the robot 10 coincides with timing in which the backlash changes inthe joint portions. In such joint portions, the operation of the robot10 may be stabilized by applying the joint structure 160. On the otherhand, the joint structure 160 may not need to be applied in, forexample, joint portions in which the changing of the backlash occursbecause the distal side link 140B constitutes a cantilever, but does notlead to the destabilization of the operation because the changing of thebacklash occurs while the robot 10 is supported by two legs in bipedalwalking, for example, and joint portions in which the changing of thebacklash does not occur under assumed control. However, conditionsdiffer in cases where the robot 10 performs operation other than bipedalwalking, and conditions differ depending on which joint portions areprogrammed to operate even in cases where bipedal walking is performed.Thus, the above-described joint structure 160 may be applied to all ofthe joint portions 130 coupling the main body side link 140A and thedistal side link 140B to each other.

(Example of Application of Joint Structure in Arm Portions)

FIG. 9A and FIG. 9B are diagrams of assistance in explaining an exampleof application of the joint structure 160 described above with referenceto FIG. 7 in the left arm portion 103L of the robot 10 according to oneembodiment of the present invention. FIG. 9A depicts a state in whichthe robot 10 has extended the left arm portion 103L horizontally, andthe palm of the hand portion 104L is directed upward. In this state, thewrist link 144L constitutes a cantilever supported by the wrist jointportion 133L. However, at this point in time, the tension spring 161 ofthe joint structure 160 including the pitch joint portion 133L_P of thewrist joint portion 133L provides a rotational biasing force in the samedirection as the gravity acting on the link 144L. Hence, in the pitchjoint portion 133L_P, a backlash BL_(PALM) on a palm side (upper side inFIG. 9A) occurs according to the gravity acting on the link 144L.

FIG. 9B depicts a state in which the yaw joint portion 132L_Y of theelbow joint portion 132L is rotated by approximately 180 degrees fromthe state depicted in FIG. 9A. In this state, the wrist link 144Lcontinues to constitute a cantilever supported by the wrist jointportion 133L. However, as a result of the rotation of a part on aterminal side of the yaw joint portion 132L_Y of the arm portion 103L by180 degrees, the palm of the hand portion 104L is directed downwardunlike the state of FIG. 9A. Here, as a result of the rotation of thejoint structure 160 including the pitch joint portion 133L_P of thewrist joint portion 133L by 180 degrees, the tension spring 161 providesa rotational biasing force in a direction countering the gravity actingon the link 144L. The backlash occurring in the pitch joint portion133L_P is consequently maintained to be the backlash BL_(PALM) on thepalm side (lower side in FIG. 9B).

In cases where the joint structure 160 is applied to the joint portionsof the arm portions 103L and 103R of the robot 10 as in theabove-described example, the backlash can be prevented from changing inthe joint portion 130 even when the direction of the gravity applied tothe distal side link 140B is changed by operation of another jointportion, for example. It is thereby possible to control the positions ofthe hand portions 104L and 104R, for example, with high accuracyirrespective of operation of the other joint portions, and improveaccuracy of an operation of the robot 10 which operation is an operationof holding another object with the hand portions 104L and 104R or movinganother object.

In addition, as can be said from the above-described example, thetension spring 161 of the joint structure 160 does not necessarilyprovide a rotational biasing force that counters the gravity acting onthe distal side link 140B at all times while the distal side link 140Bconstitutes a cantilever having the joint portion 130 as a fulcrum. Forexample, in a case where the orientation of the distal side link 140Bwith respect to a gravitational direction changes as in the exampledescribed above with reference to FIG. 9A and FIG. 9B, the tensionspring 161 may be configured to provide a rotational biasing force thatcounters the gravity in a specific direction which gravity acts on thedistal side link 140B. In this case, the tension spring 161 may providea rotational biasing force in the same direction as the gravity actingon the distal side link 140B while the gravity acting on the distal sidelink 140B is not in the specific direction.

(Modifications of Joint Structure)

FIG. 10A and FIG. 10B are diagrams depicting modifications of the jointstructure of the robot according to one embodiment of the presentinvention, the joint structure having been described above withreference to FIG. 7. A joint structure 160A according to a modificationdepicted in FIG. 10A includes a coupling member 162A coupled to thefirst part 130A of the joint portion 130 and a tension spring 161A. Bothends of the tension spring 161A are respectively coupled to the couplingmember 162A and the distal side link 140B. The tension spring 161A isattached between the coupling member 162A and the distal side link 140Bin a state of being expanded in advance. A tensile biasing forcetherefore occurs so as to rotate the distal side link 140B and bring thedistal side link 140B close to the coupling member 162A. As describedabove, the coupling member 162A and the distal side link 140B arerespectively coupled to the first part 130A and the second part 130B ofthe joint portion 130. Thus, a rotational biasing force coaxial with therelative rotation of the second part 130B with respect to the first part130A is provided by the biasing force that the tension spring 161Aapplies to the coupling member 162A and the distal side link 140B asdescribed above.

Here, in the modification depicted in FIG. 10A, unlike the exampledepicted in FIG. 7, one end of the tension spring 161A is coupled to thecoupling member 162A coupled to the first part 130A rather than to themain body side link 140A. Thus, as long as a rotational biasing force isultimately applied to the second part 130B, both ends of the tensionspring 161A may be coupled to the main body side link 140A and thedistal side link 140B, may be coupled to the coupling member coupled tothe first part 130A or the second part 130B, or may be coupled directlyto the first part 130A or the second part 130B.

In addition, while the tension spring 161 extends along an arc centeredon the rotational axis X (by using a spring guide not depicted, forexample) in the modification depicted in FIG. 7, the tension spring 161Aextends linearly in the modification depicted in FIG. 10A. Thus, thetension spring 161A may not be arranged such that the tension spring161A itself produces a rotational biasing force about the rotationalaxis X. Specifically, for example, utilizing a fact that the first part130A and the second part 130B of the joint portion 130 are assembled soas to be rotatable relative to each other about the rotational axis X,the tension spring 161A may provide a linear biasing force to the secondpart 130B or a part coupled to the second part 130B such that arotational biasing force about the rotational axis X is ultimatelyapplied to the second part 130B.

On the other hand, in a joint structure 160B according to a modificationdepicted in FIG. 10B, as compared with the modification depicted in FIG.10A, a solenoid actuator 163B is attached to the coupling member 162A,and the tension spring 161A is coupled to the solenoid actuator 163B.The solenoid actuator 163B operates in a predetermined stroke in atangential direction of a circle centered on the rotational axis X, andthereby expands or contracts the tension spring 161A as an elastic bodyconstituting biasing means. The length of the tension spring 161A andthe position of the coupling member 162A are set such that a linearbiasing force that can counter the force F acting on the distal sidelink 140B is applied when the solenoid actuator 163B expands the tensionspring 161A, and such that the linear biasing force that can counter theforce F acting on the distal side link 140B is not applied when thesolenoid actuator 163B contracts the tension spring 161A.

That is, in the example of FIG. 10B, the solenoid actuator 163Bfunctions as switching means for switching between a first state inwhich the tension spring 161A applies a sufficient rotational biasingforce to the second part 130B of the joint portion 130 and a secondstate in which the tension spring 161A does not apply the sufficientrotational biasing force to the second part 130B. In the above-describedfirst state, the position of the backlash BL in the joint portion 130 isdetermined by the biasing force of the tension spring 161A irrespectiveof the direction of the force F acting on the distal side link 140B. Onthe other hand, in the above-described second state, the position of thebacklash BL in the joint portion 130 is determined by the direction ofthe force F acting on the distal side link 140B.

Incidentally, the switching means included in the joint structure 160Bis not limited to a solenoid actuator, but may be another kind of linearactuator that can expand or contract the tension spring 161A.Alternatively, the switching means may be a rotary actuator that canexpand or contract the tension spring 161A by winding up a wire or abelt coupled to the tension spring 161A. As will be described later,other biasing means can be used in place of the tension spring 161A.Also in that case, when the biasing means is an elastic body, amechanism of expanding or contracting the elastic body, such as theabove-described solenoid actuator 163B or the like, can be used as theswitching means.

With the use of the joint structure 160B as described above, in anexample of bipedal walking as described above with reference to FIG. 8Aand FIG. 8B, for example, a rotational biasing force may be applied tothe roll joint portions 134L_R and 134R_R while the robot 10 issupported by one leg (that is, while any one of the leg portions 105Land 105R is raised), whereas the rotational biasing force may not beapplied while the robot 10 is supported by both legs. While the robot 10is supported by both legs, there is a relatively small possibility thatthe operation of the robot 10 becomes unstable even when the changing ofthe backlash in the joint portion occurs. Thus, with the use of theswitching means, the operation of the robot 10 may be stabilized by therotational biasing force by selecting the above-described first state ina critical situation in the operation of the robot 10, whereas therotational biasing force may be prevented from producing an unexpectedeffect on the operation of the robot 10 in other situations by selectingthe second state.

Incidentally, in the joint structure of the robot 10 described above,the tension spring 161 (or the tension spring 161A) is an example of thebiasing means for applying the rotational biasing force to the secondpart 130B of the joint portion 130. Specifically, the tension spring 161(or the tension spring 161A) can be an elastic body such as variouskinds of springs including a coil spring, a spiral spring, and the likeor a rubber band or the like. In the above-described example, therotational biasing force is applied to the second part 130B by a tensilebiasing force produced by the tension spring 161. However, when theposition of the tension spring 161 with respect to the distal side link140B is reversed, for example, the rotational biasing force can beapplied to the second part 130B by a compressive biasing force producedby the tension spring 161.

(Calibration of Potentiometer)

The potentiometer 155 described above with reference to FIG. 3 is asensor that detects relative rotation occurring between the two linkscoupled to the joint portion 130. The output voltage of thepotentiometer 155 changes according to the rotational angle of a part ofthe joint portion 130 to which the potentiometer 155 is attached (whichpart is, for example, the second part 130B described above withreference to FIG. 5A and FIG. 5B and the like). The control device 110of the robot 10 recognizes an actual rotational angle in the jointportion 130 by a digital signal based on the output voltage.

FIG. 11 is a graph of assistance in explaining an example of calibrationof the potentiometer. In the graph of FIG. 11, an axis of abscissasindicates the rotational angle θ of the joint portion 130 to which thepotentiometer 155 is attached, and an axis of ordinates indicates theoutput voltage V of the potentiometer 155. In the illustrated example,the output voltage V changes according to a function f(θ)₀ with respectto the rotational angle θ. The function f(θ)₀ varies according to anindividual difference of the potentiometer 155 or the like. Thus,calibration of the potentiometer 155 is needed to convert the outputvoltage V to the rotational angle θ.

In the illustrated example, for three rotational angles θ1, θ₂, and θ₃,output voltages V₁, V₂, and V₃ at the rotational angles are measured,and a function f(θ)₁ approximate to relation between the rotationalangle θ and the output voltage V is obtained from a result of themeasurement. The function f(θ)₁ in the illustrated example is anapproximate straight line determined with the point (θ₁, V₁), the point(θ₂, V₂), and the point (θ₃, V₃) as a reference. The definition of sucha function f(θ)₁ enables conversion of the output voltage V to theestimated value of the rotational angle θ by setting θ=f⁻¹(V)₁ even whenthe output voltage V of the potentiometer 155 is an arbitrary valueother than the output voltages V₁, V₂, and V₃. Incidentally, in thefollowing description, this function f⁻¹(V)₁ will be referred to also asa conversion function obtained by calibration of the potentiometer 155.

However, as depicted in the figure, the function f(θ)₀ indicating theoriginal output voltage V of the potentiometer 155 with respect to therotational angle θ is not necessarily a linear function. Hence, there isa possibility of occurrence of a larger difference V_(DIFF) between theoriginal function f(θ)₀ and the function f(θ)₁ at rotational angles(illustrated as a range between a rotational angle θ, and a rotationalangle θ_(y) in FIG. 11) different from the three rotational angles θ₁,θ₂, and θ₃ serving as references for determining the function f(θ)₁, forexample. In the range of such rotational angles θ, there is apossibility that a difference is present between the estimated value ofthe rotational angle θ on the basis of the conversion function f⁻¹(V)₁and the actual rotational angle θ, that is, there is a possibility thatthe estimated value of the rotational angle θ on the basis of the outputvoltage V of the potentiometer 155 is not necessarily accurate.

Here, as described with reference to FIGS. 6A to 6C described above orthe like, in the operation of the robot 10, there is a situation inwhich an unexpected moment or vibration (even if the moment or thevibration is small) leads to a result such as toppling over of the robot10 or the like, such as a situation of switching between support by bothlegs and support by one leg in bipedal walking, for example. In thefollowing description, such a situation will be referred to also as acritical situation in the operation of the robot 10. In a case where thedifference V_(DIFF) as depicted in FIG. 11 occurs at a rotational anglein a critical situation in the operation of the robot 10, for example,there is a possibility that a result such as toppling over or the likeoccurs easily because the estimated value of the rotational angle θ usedfor the control device 110 to control the robot 10 is not accurate.

As described above with reference to FIG. 3, the control device 110extracts a difference between the ideal value of the rotational angle ofthe joint portion 130 and the actually occurring rotational angle θ bycomparing the target value of the rotational angle of the motor 150which target value is input to the servo circuit 151 and the rotationalangle θ detected by the potentiometer 155. When this difference islarge, the control device 110 inputs an additional target value forcompensating for the difference to the servo circuit 151. Such controlcan appropriately control the operation of the robot 10 by reducing theeffect of the backlash occurring in the driving force transmittingmechanism 154 that transmits a rotational driving force from the motor150 to the joint portion 130, for example. However, as alreadydescribed, the rotational angle θ used by the control device 110 tocontrol the robot 10 is the estimated value converted from the outputvoltage V by using the conversion function f⁻¹(V)₁. Hence, when theestimated value of the rotational angle θ is not accurate due to thedifference V_(DIFF) depicted in FIG. 11, for example, there is apossibility that the operation of the robot 10 is not controlledappropriately because an additional target value that is supposed benecessary is not input or an additional target value that is supposed tobe unnecessary is input.

Meanwhile, the control device 110 can also recognize states such as theposture and inclination of the robot 10, contact of the foot portions106L and 106R with the floor surface, and the like via sensors such asthe IMU 125 and the grounding confirming sensors 126L and 126R describedabove with reference to FIG. 2 or the like. The detected values of thesesensors, for example, may be used to control the operation of the robot10 appropriately in a critical situation as described above. Forexample, during support by one leg in bipedal walking, the operation ofthe robot 10 can be controlled appropriately without being affected bythe difference V_(DIFF) depicted in FIG. 11 by controlling therotational angle θ of the joint portion 130 while constantly checkingthe posture of the robot 10 by referring to the detected value of theIMU 125. However, control of feeding back the posture of the robot 10which posture is detected by the IMU 125 as described above imposes aheavy processing load on the CPU 111. Unlike a relatively simple controlof compensating for a difference in the rotational angle, the processingload is increased greatly by incorporating a physical quantityindicating the posture of the robot 10 (which physical quantity isspecifically acceleration and angular velocity) into parameters forcontrol.

(Application of Offset Value to Calibration Result)

FIG. 12 is a graph of assistance in explaining application of an offsetvalue to a potentiometer calibration result in one embodiment of thepresent invention. In an example depicted in the graph of FIG. 12, afunction f(θ)₂ obtained by adding an offset value V_(OFFSET) to thevalue of the function f(θ)₁ is used to convert the output voltage V ofthe potentiometer 155 to the rotational angle θ in the range between therotational angle θ, and the rotational angle θ. In the illustratedexample, the offset value V_(OFFSET) compensates for a differencebetween the function f(θ)₀ and the function f(θ)₂ in the range betweenthe rotational angle θ, and the rotational angle θ.

When the range between the rotational angle θ, and the rotational angleθ_(y) is a range of rotational angles θ in a critical situation in theoperation of the robot 10, for example, the application of the offsetvalue V_(OFFSET) compensates for the difference between the estimatedvalue of the rotational angle θ in the case of using the conversionfunction f⁻¹(V)₁ in this range and the actual rotational angle θ. As aresult, the control device 110 can recognize an accurate rotationalangle θ in this range, and control the operation of the robot 10 moreappropriately. On the other hand, in the example of FIG. 12, the offsetvalue V_(OFFSET) is applied in a limited manner in the range between therotational angle θ_(x) and the rotational angle θ_(y). That is, theoriginal function f(θ)₁ and the conversion function f⁻¹(V)₁ are used atrotational angles θ_(x) other than the range between the rotationalangle θ_(x) and the rotational angle θ_(y). However, the rotationalangle θ_(x) and the rotational angle θ_(y) may not necessarily bedetected directly. For example, as in an example of a setting procedureto be described later, when a critical situation in operation isidentified by using another sensor possessed by the robot 10, such asthe IMU 125 or the like, and the offset value V_(OFFSET) is applied in alimited manner in the situation, the offset value V_(OFFSET) isultimately applied in a limited manner in the range between therotational angle θ_(x) and the rotational angle θ_(y). In this case, theapplication of the offset value V_(OFFSET) in a limited manner in thespecific range of rotational angles θ is equivalent to the applicationof the offset value V_(OFFSET) in a limited manner in a criticalsituation in the operation of the robot 10.

It is to be noted that in one embodiment of the present invention whichembodiment will be described in the following, recognition of anaccurate rotational angle θ on the basis of the output voltage V of thepotentiometer 155 is made possible by applying the offset valueV_(OFFSET) to the conversion function f⁻¹(V)₁ and thus setting afunction f⁻¹(V+V_(OFFSET))₁ equivalent to a conversion function f⁻¹(V)₂,rather than replacing the conversion function f¹(V)₁ with the conversionfunction f⁻¹(V)₂. Such a configuration is, for example, advantageous forapplying the offset value V_(OFFSET) in a limited manner in a criticalsituation in the operation of the robot 10 as described above, applyingdifferent offset values V_(OFFSET) for respective critical situations ina plurality of operations of the robot 10, or updating the offset valueV_(OFFSET) so as to correspond to a change in the function f(θ)₀ due toa secular change in the potentiometer 155 or a surrounding environment.

FIG. 13 is a flowchart depicting an example of a concrete procedure forsetting and applying the offset value in one embodiment of the presentinvention. Incidentally, suppose that in the illustrated processing, theconversion function f⁻¹(V)₁ is determined in advance by separatecalibration processing.

First, the CPU 111 starts a bipedal walking operation of the robot 10(step S101). Here, the CPU 111 controls the motor 150 thatrotation-drives the joint portion 130 of each part of the robot 10according to a bipedal walking control pattern read from the ROM 113 orthe external memory 114. At this point in time, the CPU 111 converts theoutput voltage V of the potentiometer 155 to the estimated value of therotational angle θ according to the conversion function f⁻¹(V)₁.

Here, when the grounding confirming sensors 126L and 126R detect thatany one of the foot portions 106L and 106R of the robot 10 is not incontact with the floor surface, that is, that the robot 10 is supportedby one leg (step S102), and the offset value V_(OFFSET) for bipedalwalking is yet to be set (step S103), the CPU 111 performs a procedurefor setting the offset value V_(OFFSET). Specifically, the CPU 111recognizes the posture of the robot 10 by referring to a detectionresult of the IMU 125 (step S104), and determines the offset valueV_(OFFSET) on the basis of a difference between an actual posture and anideal posture of the robot 10 (for example, an angle of inclination ofthe actual posture with respect to the ideal posture) (step S105). Here,the ideal posture of the robot 10 in bipedal walking can be a posturesuch that the main body portion 102 is horizontal, for example.

At the point in time of step S104 described above, the CPU 111 controlsthe bipedal walking operation of the robot 10 according to the estimatedvalue of the rotational angle θ converted from the output voltage V byusing the conversion function f¹(V)₁ without applying the offset valueV_(OFFSET). Here, when there is a difference between the actualrotational angle θ and the above-described estimated value, a differencecorresponding to the difference in the rotational angle θ occurs also ina result of the control, that is, between the actual posture and theideal posture of the robot 10. Accordingly, in step S105, the CPU 111determines the offset value V_(OFFSET) on the basis of the differencebetween the actual posture and the ideal posture of the robot 10. It ismade possible to compensate for the difference between the actuallyoccurring rotational angle θ and the recognition result in theabove-described case, and maintain an appropriate posture of the robot10 by the control of the CPU 111 as described above. Specifically, forexample, the CPU 111 calculates the offset value V_(OFFSET) for therotational angle θ of each joint portion by converting the inclinationof the actual posture with respect to the appropriate posture intorotations (a pitch rotation, a roll rotation, and a yaw rotation) in thejoint portions of the leg portions 105L and 105R.

When the offset value V_(OFFSET) is calculated in step S105 describedabove, and when the offset value V_(OFFSET) is already set in step S103described above, the CPU 111 applies the offset value V_(OFFSET) inconverting the output voltage V to the estimated value of the rotationalangle θ (step S106). Specifically, the CPU 111 sets the functionf⁻¹(V+V_(OFFSET))₁ by applying the offset value V_(OFFSET) to theconversion function f⁻¹(V)₁, and then converts the output voltage V tothe estimated value of the rotational angle θ. Consequently, theestimated value of the rotational angle 0 approaches the actualrotational angle θ, and the CPU 111 can control the bipedal walkingoperation of the robot 10 more appropriately.

When the grounding confirming sensors 126L and 126R detect in step S102described above that the robot 10 is not supported by one leg, that is,the robot 10 is supported by both legs, on the other hand, the CPU 111converts the output voltage V to the rotational angle θ according to theconversion function f⁻¹(V)₁ without applying the offset value V_(OFFSET)(step S107). The above processing is thereafter repeated until the CPU111 ends the bipedal walking operation of the robot 10 (step S108).

The processing according to the present embodiment as described abovecan obtain the estimated value of the rotational angle θ in which theeffect of the difference V_(DIFF) depicted in FIG. 11 is reduced orremoved by applying the offset value V_(OFFSET). In addition, though thedetection result of the IMU 125 is referred to when the offset valueV_(OFFSET) is set first, a relative simple control of compensating forthe difference between the estimated value of the rotational angle θ onthe basis of the output voltage V of the potentiometer 155 and the idealvalue of the rotational angle θ is thereafter performed. Thus, aprocessing load on the CPU 111 is greatly reduced.

In addition, while the above description has been made of an example inwhich the procedure for setting the offset value V_(OFFSET) is performedat the time of a first bipedal walking operation, the CPU 111 may updatethe offset value V_(OFFSET) at predetermined intervals by periodicallyperforming the procedure for setting the offset value V_(OFFSET). Thus,even when the function f(θ)₀ changes according to a secular change inthe potentiometer 155 or the surrounding environment, for example, theoffset value V_(OFFSET) corresponding to such a change can be set. Theprocedure for setting the offset value V_(OFFSET) is easy as comparedwith a procedure of performing calibration of the potentiometer 155again and defining the function f(θ)₁ again, for example, and theprocedure for setting the offset value V_(OFFSET) can be performedduring normal operation of the robot 10. Hence, in a case where an enduser uses the robot 10 at hand over a long period, for example, accurateoperation of the robot 10 can be maintained without an increase in thelabor of maintenance.

(Selective Application of Plurality of Offset Values)

FIG. 14 is a graph of assistance in explaining an example of selectivelyapplying a plurality of offset values to a potentiometer calibrationresult in one embodiment of the present invention. The graph of FIG. 14depicts a function f(θ)₃ obtained by adding a second offset valueV_(OFFSET2) to the value of the function f(θ)₁ in addition to a functionf(θ)₂ obtained by adding a first offset value V_(OFFSET1) to the valueof the function f(θ)₁. Here, as with the offset value V_(OFFSET)depicted in FIG. 12 described above, the first offset value V_(OFFSET1)compensates for a difference between the function f(θ)₀ and the functionf(θ)₂ in the range between the rotational angle θ_(x) and the rotationalangle θ_(y). On the other hand, the second offset value V_(OFFSET2)compensates for a difference between the function f(θ)₀ and the functionf(θ)₃ in a range between a rotational angle θ_(z) and a rotational angleθ_(w) different from the foregoing.

When the range between the rotational angle θ_(z) and the rotationalangle θ_(w) is a range of rotational angles θ in a critical situation inthe operation of the robot 10, the range being different from the rangebetween the rotational angle θ_(x) and the rotational angle θ_(y), forexample, the application of the second offset value V_(OFFSET2)compensates for a difference between the estimated value of therotational angle θ in a case where the conversion function f⁻¹(V)₁ isused in this range and the actual rotational angle θ. As a result, thecontrol device 110 can recognize an accurate rotational angle θ in thisrange, and control the operation of the robot 10 more appropriately.

Specifically, for example, the range between the rotational angle θ_(x)and the rotational angle θ_(y) can be a range of rotational angles θ ina critical situation in a first operation of the robot 10, for example asituation of support by one leg in bipedal walking, and the rangebetween the rotational angle θ_(z) and the rotational angle θ_(w) can bea range of rotational angles θ in a critical situation in a secondoperation of the robot 10, for example, a situation in which the robot10 rises from a seated or toppled-over state. As described above, in thepresent embodiment, the CPU 111 selects a pattern corresponding to adetermined operation from control patterns stored in the ROM 113 or theexternal memory 114, and controls the robot 10 according to the selectedpattern. Thus, in the above-described example, bipedal walking as thefirst operation and rising as the second operation can be identified onthe basis of the control pattern being selected.

Here, in applying the first offset value V_(OFFSET1) or the secondoffset value V_(OFFSET2), the CPU 111 may apply the offset value in alimited manner in a specific range of rotational angles θ (specifically,the range between the rotational angle θ_(x) and the rotational angleθ_(y) in the case of the first offset value V_(OFFSET1) and the rangebetween the rotational angle θ_(z) and the rotational angle θ_(w) in thecase of the second offset value V_(OFFSET2)), or may apply the firstoffset value V_(OFFSET1) or the second offset value V_(OFFSET2) in theentire range of rotational angles θ in a case where a specific controlpattern (the bipedal walking pattern and the rising pattern in theabove-described concrete example) is selected, as depicted in FIG. 14.

FIG. 15 is a flowchart depicting an example of a concrete procedure forselectively applying a plurality of offset values in one embodiment ofthe present invention. Incidentally, suppose that in the illustratedprocessing, the first offset value V_(OFFSET1) for bipedal walking andthe second offset value V_(OFFSET2) for rising are determined in advanceby performing the setting procedure as illustrated above in FIG. 13 foreach of the first offset value V_(OFFSET1) and the second offset valueV_(OFFSET2), and are stored in the ROM 113 or the external memory 114.In addition, suppose that processing of recognizing the rotational angleθ of the joint portion 130 after applying each of the offset values issimilar to the processing illustrated in FIG. 13.

First, when a bipedal walking pattern is selected as a control patternof the robot 10 (step S111), the CPU 111 applies the first offset valueV_(OFFSET1) (step S112). Thus, during the bipedal walking operation ofthe robot 10, the CPU 111 recognizes the rotational angle θ from theoutput voltage V of the potentiometer 155 according to the functionf(θ)₂ to which the first offset value V_(OFFSET1) is applied.

When a rising pattern is selected as a control pattern of the robot 10(step S113), on the other hand, the CPU 111 applies the second offsetvalue V_(OFFSET2) (step S114). Thus, during the rising operation of therobot 10, the CPU 111 recognizes the rotational angle θ from the outputvoltage V of the potentiometer 155 according to the function f(θ)₃ towhich the second offset value V_(OFFSET2) is applied.

When neither of the bipedal walking pattern or the rising pattern isselected as a control pattern of the robot 10 as a result of thedetermination in step S111 or S113 described above, the CPU 111recognizes the rotational angle θ from the output voltage V of thepotentiometer 155 according to the function f(θ)₁ to which no offsetvalue is applied.

With the processing as described above, in critical situations in aplurality of operations of the robot 10, the selective application ofthe plurality of offset values enables the CPU 111 to recognize therotational angle θ accurately, and control the operation of the robot 10appropriately by a relatively simple control of compensating for adifference between the ideal value of the rotational angle and theactually occurring rotational angle θ.

Incidentally, with regard to the operation of the robot 10, an operationof bipedal walking and an operation of rising from a state in which therobot 10 is seated or toppled over have been illustrated in the abovedescription. However, the operation of the robot 10 is not limited tosuch examples. In addition, critical situations in the respectiveoperations are not limited to examples in the above description. Forexample, a critical situation in bipedal walking may be defined as asituation in which a ZMP is on a boundary line of a stable region. Inaddition, the above-described examples are examples in which mainly therotational angles at the joint portions of the leg portions 105L and105R and the foot portions 106L and 106R affect a result of operation ofthe robot 10. However, there can be a case where the rotational anglesat the joint portions of the arm portions 103L and 103R and the handportions 104L and 104R affect a result of operation of the robot 10. Forexample, in an operation of grasping an object of a known size, theobject can be grasped while a force exerted on the object is reduced toa necessary minimum by accurately controlling the rotational angle θ inthe grasping situation. In addition, in an operation when the robot 10reproduces an arbitrary programmed motion, the motion can be reproducedwithout causing interference between parts of the robot 10 by accuratelycontrolling the rotational angle θ in a situation in which there is apossibility that the parts of the robot 10 interfere with each other,such, for example, as a situation in which both arms are made tointersect each other or the like.

In addition, in the example described with reference to FIG. 15described above, the operation of the robot 10 includes the firstoperation (bipedal walking) and the second operation (rising), and theoffset value includes the first offset value (V_(OFFSET1)) correspondingto a critical situation in the first operation and the second offsetvalue (V_(OFFSET2)) corresponding to a critical situation in the secondoperation. However, relation between the operation of the robot 10 andthe critical situation in the operation and the offset value is notlimited to such an example. For example, in a single operation of therobot 10, there may be a first critical situation and a second criticalsituation, and a first offset value and a second offset valuecorresponding to the respective critical situations may be set.

In addition, the above description has been made of an example in whichthe offset value V_(OFFSET) is applied to a result of calibration of thepotentiometer 155 as a sensor that detects the rotational angle θ in thejoint portion 130 of the robot 10. However, a similar configuration maybe applied to a sensor that detects another state quantity of the robot10. For example, it can be useful to apply an offset value set so as tocompensate for a difference between an estimated value and an actualvalue in a critical situation occurring in the operation of the robot10, for example, to various kinds of sensors in which relation betweenstate quantities detected by the sensors and the detected values of thesensors is not necessarily linear as described with reference to FIG.11, and calibration is therefore necessary to convert the detectedvalues to the estimated values of the state quantities.

Illustrative embodiments of the present invention have been describedabove. Incidentally, the configurations of the embodiments describedabove can be implemented independently of each other or in combinationwith each other. Specifically, for example, the joint structure asdescribed with reference to FIG. 7 can be implemented independent of theapplication of the offset value as described with reference to FIG. 12.Also in the example of the joint structure, the application thereof inthe leg portions 105L and 105R of the robot 10 as depicted in FIG. 8Aand FIG. 8B and the application thereof in the arm portions 103L and103R of the robot 10 as depicted in FIG. 9A and FIG. 9B may both beimplemented, or either the application thereof in the leg portions 105Land 105R of the robot 10 as depicted in FIG. 8A and FIG. 8B or theapplication thereof in the arm portions 103L and 103R of the robot 10 asdepicted in FIG. 9A and FIG. 9B may be implemented.

In addition, the above description has been made by genericallyillustrating the joint portion 130 of the robot 10 or illustrating apart of the joint portions (for example, the crotch roll joint portion134L_R). However, the structure or control as described can be appliedin each of the joint portions of the robot 10 as described withreference to FIG. 1 according to the operation of the robot 10 andcontrol for realizing the operation. In addition, the jointconfiguration of the robot 10 depicted in FIG. 1 is an example, andvarious other joint configurations are also possible. In addition,robots according to other embodiments of the present invention are notlimited to humanoid robots such as the robot 10 depicted in FIG. 1 andthe like, but can be various kinds of robots that have a joint portionand in which there is a critical situation in an operation realized bycontrol of the joint portion such that the joint portion is subjected toan effect of a backlash.

A few embodiments of the present invention have been described above indetail with reference to the accompanying drawings. However, the presentinvention is not limited to such examples. It is obvious that a personhaving an ordinary knowledge in the technical field of the presentinvention could conceive of various changes or modifications within thescope of technical concepts described in claims. It is therefore to beunderstood that these changes or modifications also naturally fallwithin the technical scope of the present invention.

REFERENCE SIGNS LIST

10 . . . Robot, 101 . . . Head portion, 102 . . . Main body portion,103L, 103R . . . Arm portion, 104L, 104R . . . Hand portion, 105L, 105R. . . Leg portion, 106L, 106R . . . Foot portion, 110 . . . Controldevice, 111 . . . CPU, 113 . . . ROM, 114 . . . External memory, 115 . .. Bus interface, 116 . . . Conversion function, 117 . . . Offset value,130 . . . Joint portion, 130A . . . First part, 130B . . . Second part,140A . . . Main body side link, 140B . . . Distal side link, 150 . . .Motor, 151 . . . Servo circuit, 152 . . . Driver, 153 . . . Encoder, 154. . . Driving force transmitting mechanism, 155 . . . Potentiometer, 156. . . A/D converter circuit, 160 . . . Joint structure, 161, 161A . . .Tension spring, 162A . . . Coupling member, 163B . . . Solenoidactuator.

1. A joint structure for a robot, the joint structure comprising: ajoint portion including a first part coupled to a main body side linkand a second part coupled to a distal side link; a driving forcetransmitting mechanism configured to transmit, to the joint portion, arotational driving force causing relative rotation of the second partwith respect to the first part; and biasing means for applying arotational biasing force coaxial with the relative rotation to thesecond part, wherein the rotational biasing force counters gravityacting on the distal side link when the distal side link constitutes acantilever having the joint portion as a fulcrum.
 2. (canceled)
 3. Thejoint structure for a robot according to claim 21, wherein the distalside link is included in a leg portion of the robot, and the rotationalbiasing force prevents a change in a position of a backlash in the jointportion when a transition is made between a first state in which thedistal side link does not constitute the cantilever and a second statein which the distal side link constitutes the cantilever during bipedalwalking operation of the robot.
 4. The joint structure for a robotaccording to claim 21, wherein the distal side link is included in anarm portion of the robot, and the rotational biasing force prevents achange in a position of a backlash in the joint portion when anorientation of the distal side link constituting the cantilever withrespect to a gravitational direction changes.
 5. The joint structure fora robot according to claim 1, further comprising: switching means forswitching between a first state in which the biasing means applies therotational biasing force to the second part and a second state in whichthe biasing means does not apply the rotational biasing force to thesecond part.
 6. The joint structure for a robot according to claim 5,wherein the biasing means includes an elastic body, and the switchingmeans includes a mechanism of expanding or contracting the elastic body.7. The joint structure for a robot according to claim 5, wherein theswitching means selects the first state in a critical situation inoperation of the robot, and selects the second state in othersituations.